It has been shown that male factor is a contributory cause of infertility in about 40% to 50% of the infertile couples. The overwhelming majority of these infertile and subfertile men are oligospermic and/or asthenospermic (sperm motility is lower than 50%). Management problems exist with respect to these infertile men, as these men may try to be fathers for years without success. With intrauterine placement of the sperm, the pregnancy rates for couples with male factor infertility are only at about 15-20% per cycle. This is in spite of the fact that there is no detectable difference in sperm concentrations and motility among the groups of husbands who do or do not cause pregnancy following intrauterine insemination treatment. Although the pregnancy rates with in vitro fertilization treatment are relatively high, but adequate sperm concentration or sperm motility does not assure the success of pregnancies. There are also men who suffer from unexplained male infertility problems, i.e. sperm with diminished fertility in spite of normal sperm concentrations.
Artificial insemination has become a much more frequent procedure due to a variety of sociological, economic, and perhaps environmental reasons. The number of inseminations worldwide has been increasing, and will likely continue to increase. A number of causes have been cited for this increase. For example, the increased age often lower the probability of fertilization for both men and women. More and more women are also raising children by themselves without a partner, and electing artificial insemination as a means of fertilization. In addition, those that would otherwise not be able to have children, now have a medical option that is relatively affordable. An additional factor may be that the sperm count among males has been declining, making fertilization more difficult. And finally, environmental factors have also been blamed for the decreased fertility of both men and woman.
There are currently a wide variety of artificial insemination methods such as, intracervical, intrauterine (IUI), intratubular and direct intraperitoneal (DIPI) insemination, gamete intrafallopian transfer (GIFT), in vitro fertilization and embryo transfer (IVFET), zygote intrafallopian transfer (such as ZIFT, PROST and TET), peritoneal oocyte and sperm transfer (POST), and sex selection, among others. As technology advances, other methods are certain to follow, however, regardless of the process; high motile sperm are always preferred. And, most of the facilities that perform the insemination do not have the resources to separate motile sperm, requiring a separate visit to facility that possesses the separation means. As an example, the Intrauterine Insemination (IUI) and In Vitro fertilization (IVF) methods attempt to mimic the reproductive process by placing sperm and eggs together in an environment conducive to fertilization, either in the womb or outside the womb. The fertilization process requires the sperm to actively invade the egg and commence fertilization. Motile sperm are much more likely to penetrate the egg.
Human semen is comprised of a heterogeneous cell population with different degrees of maturation, varying in functional quality and fertilizing ability. Ejaculated sperm are not immediately able to fertilize an egg. Rather, they must undergo a process of functional maturation known as “capacitation”. “Capacitation” is generally regarded to be a process that results in the acquisition of hyperactivated motility, and the acquisition of the ability to undergo acrosomal exocytosis. Capacitation results in two specific changes in sperm function. First, the sperm head acquires the ability to undergo acrosomal exocytosis in response to physiological ligands such as zona pellucida proteins or progesterone. Second, the flagellum of the sperm acquires a “hyperactivated” pattern of motility.
Fractionation of sperm by a density gradient centrifugation can separate these subpopulations, resulting in a considerable improvement in the quality of sperm recovered in the pellet. Several regions indicate that higher percentages of motile and morphologically normal sperm can be recovered from the pellet, in comparison with lower density fractions. Semen is composed of a heterogeneous population of sperm with varying degrees of structural and functional differentiation and normality. From Percoll gradient, three subsets of sperm (45%; L45), (65%; L65) and (90%; L90) fractions are often adapted when separating high quality sperm from normozoospermic human semen. L45 showed the poorest quality, displaying the smallest percentage of morphologically normal and motile sperm. L65 and L90 showed a time-dependent increment in capacitation-associated tyrosine phosphorylation (M. G. Buffone et al., Human Reprod Vol. 19, No. 1 pp 139-146, 2004).
The total number of sperms in one ejaculate is a measure of fertility; however, the percentage of motile sperm is more important, especially when considering alternate reproductive means. According to motility, sperms are categorized as shown in the following table:
Motility IndexDegree of MotilityType of Motility0No motility, or movement of tail with no forward progression120% or less showing forward progression (sluggish movement)220%-50% showing forward progression350%-80% showing forward progression480%-100% shown forward progression(very rapid movement)
The percentage of motile sperm showing progressive swimming movements is a measure of the fertility of the sperm sample. The higher the percentage, the higher quality of the sperm sample, and the greater the likelihood that the sample will achieve fertilization. A high quality sperm sample is important for many reasons. The process of artificial insemination is not only costly economically, but is psychologically expensive. Unsuccessful attempts have devastating effects on the patients. Higher quality sperm samples are also important considerations when the sample is subject to freezing or aqueous dilution, because these processes tend to kill or weaken the sample. Thus, only the highest quality sperm may survive the processing procedures to which the sperm are subjected.
Various methods of selecting the more active sperm have been utilized in the past, such as the swim up, swim down and Percoll density gradient centrifugation techniques. Swim-up methods are commonly used to process fresh or frozen specimens for the IUI and IVF procedures. The sperm is placed in a medium and subjected to a centrifuge process. The more motile sperm swim to a level where they can be extracted. Such methods employ multiple tube and centrifugation steps that are time consuming and can lead to a low recovery of motile sperm.
A number of methods exist for assessing motility and number of spermatozoa in a sample. One such method is microscopic analysis, which is typically performed in a hospital or commercial laboratory. More recently, however, a number of proposals have been made for test kits which are intended to simplify detection of spermatozoa. A disadvantage of these test kits is that they do not distinguish between motile and non-motile spermatozoa. This distinction is a most predictive indicator of male infertility.
U.S. Pat. No. 5,427,946 discloses a channeling apparatus, where there are inlet regions, flow channels, and nesting chambers. The sperm sample is applied at the inlet region, and only the motile sperm are capable of reaching the chambers. U.S. Pat. No. 7,179,641 provides an apparatus for separating and detecting motile spermatozoa in a liquid sample, comprises: a separation vessel including (i) an inlet region, (ii) an outlet region arranged to be opened, (iii) a separation medium into which motile spermatozoa in the sample can flow via the inlet region, and (iv) an actuator operable to open the outlet region for allowing the separation medium to flow out of the vessel through the outlet region. These prior art references are not based on the microfluidic techniques.
U.S. Pat. No. 6,929,945 provides a device including a microfluidics structure having a sample reservoir, a downstream collection region and a microchannel extending therebetween. The microchannel is dimensioned to confine sample sperm to single-direction movement within the channel, such that sperm in a semen sample placed in the sample reservoir enter and migrate along the microchannel toward and into the collection region. Brenda et al. provides a self-contained integrated microfluidic system for separating motile sperm from small samples, which comprises two sample inlets, two outlets, sorting channel and a passively driven pumping system that provides a steady flow of liquid. US Patent Publication No. 20100291535 discloses a method using a microfluidic chip to sort high motility sperm. In this prior art reference, sperm and a medium are respectively injected into a microchannel of a microfluidic chip via several inlets. However, the above prior references cannot make a distinguishable sorting to obtain different subpopulations of sperm. That is, the sperms sorted by the above prior references may include high motile sperms, low motile sperms and even no motile sperms. Moreover, the amounts of motile sperms sorted by the above prior art references cannot achieve a satisfied level.
Therefore, there is still a need to develop a device and method to sort not only sperms with higher motility and activity but also with more amounts in the targeted quality as well.